1. Technical Field
The present disclosure relates to devices for interfacing with high frequency data transfer media and, more particularly, to modular jack housing inserts, such as those that are used as interface connectors for Unshielded Twisted Pair (“UTP”) media, that advantageously compensate for and reduce electrical noise.
2. Background Art
In data transmission, the signal originally transmitted through the data transfer media is not necessarily the signal received. The received signal will consist of the original signal after being modified by various distortions and additional unwanted signals that affect the original signal between transmission and reception. These distortions and unwanted signals are commonly collectively referred to as “electrical noise,” or simply “noise.” Noise is a primary limiting factor in the performance of a communication system. Many problems may arise from the existence of noise in connection with data transmissions, such as data errors, system malfunctions and/or loss of the intended signals.
The transmission of data, by itself, generally causes unwanted noise. Such internally generated noise arises from electromagnetic energy that is induced by the electrical energy in the individual signal-carrying lines within the data transfer media and/or data transfer connecting devices, such electromagnetic energy radiating onto or toward adjacent lines in the same media or device. This cross coupling of electromagnetic energy (i.e., electromagnetic interference or EMI) from a “source” line to a “victim” line is generally referred to as “crosstalk.”
Most data transfer media consist of multiple pairs of lines bundled together. Communication systems typically incorporate many such media and connectors for data transfer. Thus, there inherently exists an opportunity for significant crosstalk interference.
Crosstalk can be categorized in one of two forms. Near end crosstalk, commonly referred to as NEXT, arises from the effects of near field capacitive (electrostatic) and inductive (magnetic) coupling between source and victim electrical transmissions. NEXT increases the additive noise at the receiver and therefore degrades the signal to noise ratio (SNR). NEXT is generally the most significant form of crosstalk because the high-energy signal from an adjacent line can induce relatively significant crosstalk into the primary signal. The other form of crosstalk is far end crosstalk, or FEXT, which arises due to capacitive and inductive coupling between the source and victim electrical devices at the far end (or opposite end) of the transmission path. FEXT is typically less of an issue because the far end interfering signal is attenuated as it traverses the loop.
Characteristics and parameters associated with electromagnetic energy waves can be derived by Maxwell's wave equations. In unbounded free space, a sinusoidal disturbance propagates as a transverse electromagnetic wave. This means that the electric field vectors are perpendicular to the magnetic field vectors lying in a plane perpendicular to the direction of the wave. As a result, crosstalk generally gives rise to a waveform shaped differently than the individual waveform(s) originally transmitted.
Unshielded Twisted Pair cable or UTP is a popular and widely use type of data transfer media. UTP is a very flexible, low cost media, and can be used for either voice or data communications. In fact, UTP is rapidly becoming the de facto standard for Local Area Networks (“LANs”) and other in-building voice and data communications applications. In a UTP, a pair of copper wires generally form the twisted pair. For example, a pair of copper wires with diameters of 0.4-0.8 mm may be twisted together and wrapped with a plastic coating to form a UTP. The twisting of the wires increases the noise immunity and reduces the bit error rate (BER) of the data transmission to some degree. Also, using two wires, rather than one, to carry each signal permits differential signaling to be used. Differential signaling is generally more immune to the effects of external electrical noise.
The non-use of cable shielding (e.g., a foil or braided metallic covering) in fabricating UTP generally increases the effects of outside interference, but also results in reduced cost, size, and installation time of the cable and associated connectors. Additionally, non-use of cable shielding in UTP fabrication generally eliminates the possibility of ground loops (i.e., current flowing in the shield because of the ground voltage at each end of the cable not being exactly the same). Ground loops may give rise to a current that induces interference within the cable, interference against which the shield was intended to protect.
The wide acceptance and use of UTP for data and voice transmission is primarily due to the large installed base, low cost and ease of new installation. Another important feature of UTP is that it can be used for varied applications, such as for Ethernet, Token Ring, FDDI, ATM, EIA-232, ISDN, analog telephone (POTS), and other types of communication. This flexibility allows the same type of cable/system components (such as data jacks, plugs, cross-patch panels, and patch cables) to be used for an entire building, unlike shielded twisted pair media (“STP”).
At present, UTP is being used for systems having increasingly higher data rates. Since demands on networks using UTP systems (e.g., 100 Mbit/s and 1200 Mbit/s transmission rates) have increased, it has become necessary to develop industry standards for higher system bandwidth performance. Systems and installations that began as simple analog telephone service and low speed network systems have now become high speed data systems. As the speeds have increased, so too has the noise.
The ANSI/TIA/EIA 568A standard defines electrical performance for systems that utilize the 1 to 100 MHz frequency bandwidth range. Exemplary data systems that utilize the 1-100 MHz frequency bandwidth range include IEEE Token Ring, Ethernet10Base-T and 100Base-T. ANSI/TIA/EIA-568 and the subsequent TSB-36 to TSB-40 standards define five categories, as shown in the following Table, for quantifying the quality of the cable (for example, only Categories 3, 4, and 5 are considered “datagrade UTP”).
                                       TABLECharacteristicCategoryspecified up to (MHz)Various Uses1NoneAlarm systems and other non-criticalapplications2NoneVoice, EIA-232, and other low speeddata31610BASE-T Ethernet, 4-Mbits/s TokenRing, 100BASE-T4, 100VG-AnyLAN, basic rate ISDN.Generally the minimum standardfor new installations.42016-Mbits/s Token Ring. Notwidely used.5100TP-PMD, SONet, OC-3 (ATM),100BASE-TX. The most popularfor new data installations.
UTP cable standards are also specified in the EIA/TIA-568 Commercial Building Telecommunications Wiring Standard, including the electrical and physical requirements for UTP, STP, coaxial cables, and optical fiber cables. For UTP, the requirements currently include:                Four individually twisted pairs per cable        Each pair has a characteristic impedance of 100 Ohms+/−15% (when measured at frequencies of 1 to 100 MHz)        24 gauge (0.5106-mm-diameter) or optionally 22 gauge (0.6438 mm diameter) copper conductors are used        
Additionally, the ANSI/EIA/TIA-568 standard specifies the color coding, cable diameter, and other electrical characteristics, such as the maximum cross-talk (i.e., how much a signal in one pair interferes with the signal in another pair—through capacitive, inductive, and other types of coupling). Since this functional property is measured as how many decibels (dB) quieter the induced signal is than the original interfering signal, larger numbers reflect better performance.
Category 5 cabling systems generally provide adequate NEXT margins to allow for the high NEXT associated with use of present UTP system components. Demands for higher frequencies, more bandwidth and improved systems (e.g., Ethernet 1000Base-T) on UTP cabling, render existing systems and methods unacceptable. The TIA/EIA category 6 draft addendum related to new category 6 cabling standards illustrates heightened performance demands. For frequency bandwidths of 1 to 250 MHz, the draft addendum requires the minimum NEXT values at 100 MHz to be −39.9 dB and −33.1 dB at 250 MHz for a channel link, and −54 dB at 100 MHz and −46 dB at 250 MHz for connecting hardware. Increasing the bandwidth for new category 6 (i.e., from −1 to 100 MHz in category 5 to 1 to 250 MHz in category 6) increases the need to review opportunities for further reducing system noise.
The standard modular jack housing is configured and dimensioned so as to provide maximum compatibility and matability between various manufacturers, e.g., based on the FCC part 68.500 mechanical dimension. Two types of offsets have been produced from the FCC part 68.500 modular jack housing dimensions.
Type one is the standard FCC part 68.500 style for modular jack housing and such standard housing does not add or include any compensation methods to reduce crosstalk noises. The standard modular jack housing utilizes a straightforward design approach and, by alignment of lead frames in a relatively uniform, parallel pattern, high NEXT and FEXT are produced for certain adjacent wire pairs.
This type one or standard FCC part 68.500 style of modular jack housing connector is defined by two lead frame section areas. The first section is the matable area for electrical plug contact and section two is the output area of the modular jack housing. Section one aligns the lead frames in a relatively uniform, parallel pattern from lead frame tip to the bend location that enters section two, thus producing high NEXT and FEXT noises. Section two also aligns the lead frames in a relatively uniform, parallel pattern from lead frame bend location to lead frame output, thus producing and allowing additional high NEXT and FEXT noises.
There have been approaches that are intended to reduce the crosstalk noises associated with these type one or standard modular jack housings. For example, U.S. Pat. No. 5,674,093 to Vaden et al. discloses an electrical connector having an irregular bend in one lead frame of each pair. The irregular bend reduces the parallelism of the lead frames to contribute to reductions in potential coupling effects. Although crosstalk noise may be reduced, forming lead frames as disclosed in the Vaden '093 patent is a complex process and the return loss and differential impedance in the circuit is disadvantageously increased for all four pairs.
The second type of modular jack housing is the standard FCC part 68.500 style for modular jack housings that incorporate compensation methods to reduce crosstalk noises. For example, U.S. Pat. No. 5,639,266 to Stewart discloses a compensation approach for modular jack housings that involves aligning the lead frames of the opposite pairs in an uniformed parallel pattern to removed crosstalk noises. The Stewart connector is defined by two lead frame section areas, section one being the matable area for electrical plug contact and section two being the output area of the modular jack housing. Stewart's section one aligns two lead frames, namely, positions 3 and 5 out of 8, in an uniformed and reversed signal parallel pattern from lead frame tip to the bend location that enters section two, thus reducing crosstalk noises by signal compensation. Section two also aligns the lead frames in an uniformed parallel pattern from lead frame bend location to lead frame stagger array output, which minimizes NEXT, but due to the imbalances of the center wire pairs 1 and 3, FEXT noises are disadvantageously increased according to the Stewart '266 design.
Another example of crosstalk compensation methodology is disclosed in U.S. Pat. No. 5,647,770 to Berg and U.S. Pat. No. 5,779,503 to Nordx/CDT. These two patents disclose compensation approaches for modular jack housings that involve aligning and re-bending the lead frames of the opposite pairs in an uniformed parallel pattern to contribute to crosstalk noise reduction. The Berg and Nordx/CDT devices utilize de facto standard rear entry pin positions of 0.1 inch separation for all pair arrays after the deformation of the wire pairs. The re-bending of lead frames as disclosed by the Berg '770 and Nordx/CDT '503 patents is an expensive process and the crosstalk reductions addressed by these disclosures occur mainly within the second section of their respective designs. Another method for crosstalk noise reduction and control in connecting hardware is addressed in commonly assigned U.S. Pat. No. 5,618,185 to Aekins, the disclosure of which is hereby incorporated by reference.
In view of the increasing performance demands being placed on UTP systems, e.g., the implementation of category 6 standards, it would be beneficial to provide a device and/or methodology that reduces NEXT and FEXT noises associated with standard FCC part 68.500 modular jack housings in a simple and cost effective manner. These and other objectives are achieved through the advantageous modular jack housings disclosed herein.